1. Field
The following description relates to a transmitter optical sub-assembly forming an optical transceiver of an optical communication system, and more particularly, to an angled physical contact receptacle stub and a transmitter optical sub-assembly having the same.
2. Description of the Related Art
An Optical sub-assembly (OSA) is manufactured by use of a cylindrical or box type housing called as a transistor-outlined (TO) CAN. TO CAN is manufactured by attaching a light source chip and a photo diode (PD) chip on a main mount, referred to as a stem, by use of a sub-mount, and then aligning an optical fiber, or an optical fiber stub or an optical fiber ferrule having an optical fiber with the optical source chip through a lens.
In particular, in manufacturing a transmitter Optical Sub-Assembly (TOSA), the coupling efficiency between the light source chip and the optical fiber is highly regarded. Accordingly, the TOSA is manufactured using an Active Alignment in which optical alignment is achieved by applying an electric current on a light source such that the optical coupling is maximized. In this case, the TOSA is manufactured by coupling optical elements, such as a metal housing and a receptacle which supports an optical fiber ferrule, through laser welding. The shape of the OSA is determined by standards of optical transceiver for customization and industrialization, and the OSA is connected to a transmission fiber through standardized input/output optical connectors.
Optical connectors, which have been commercialized and widely used, are classified into a Subscriber Connector or Square Connector (SC), a Fiber Transmission System Connector (FC), a Lucent Connector (LC), a Straight Tip (ST) and a Miniature Unit (MU) based on the external shape, and classified into a Physical Contact (PC) connector and an Angled Physical Contact (APC) connector based on the shape of a polished end section of a fiber ferrule of a connector.
The PC connector is finely classified into a Super Physical Contact (SPC) and a Ultra Physical Contact (UPC) based on the degree of reflection occurring when two connectors are physically coupled to each other. If an air gap exists due to an imperfect coupling between PC end sections, the reflectivity at the end sections is substantially increased. The APC connector has an end section angled with about 6° to 8° to improve the reflection characteristics or return loss, thereby preventing the transmission efficiency from being degraded due to reflection at the end section.
For a colorless light source that is sensitive to reflection, for example, a Reflective Semiconductor Optical Amplifier (RSOA), and a Reflective Electro-Absorption Modulator (REAM), a transceiver is manufactured by use of a fiber pigtail type TOSA having an APC connector. However, in a wavelength division multiplexing-passive optical network (WDM-PON) system, the using of the fiber pigtail type TOSA in an optical transceiver increases the volume of the optical transceiver and lowering the mounting density of a system
In addition, the using of the fiber pigtail type TOSA does not satisfy the shape of an optical transceiver that is suggested by standardization organization such as Multi-Source Agreement, increasing the complexity of the system. In addition, an additional device or equipment needs to be installed to accommodate the optical transceiver, thereby increasing the implementation cost when the system is constructed and causing unexpected problems when the system operates. In order to remove the above described drawbacks, there is a need for an APC receptacle TOSA that is applicable to a standardized transceiver.
The manufacturing of an APC receptacle TOSA requires more thorough optical alignment compared to a fiber pigtail TOSA or a PC receptacle TOSA. That is, a fiber receiving end formed at a lower part of a receptacle is generally designed to have an angled facet such that interference caused by near reflection is removed.
In achieving the maximum optical coupling by use of a fiber pigtail TOSA, a rotational alignment is performed such that a position of a beam collected through a lens corresponds to a position where an APC angle optical stub is coupled to a housing and a direction of the beam corresponds to an angle direction of Φ with respect to an axis of light propagation.
In achieving the maximum optical coupling by use of PC receptacle TOSA, different from the fiber pigtail TOSA, the PC receptacle is subject to alignment such that beam is collected in the center of an upper part of a housing to maintain a uniform shape. In this case, the fiber transmitting end, which is coupled to an external part, does not an orientation, so the PC receptacle is subject to a rotational alignment with an axis Φ in consideration of uncertainty of the direction of beam path, thereby achieving the maximum optical coupling.
In order to achieve the maximum optical coupling by use of the APC receptacle TOSA, a facet direction of the APC receptacle needs to be fixed to a predetermined direction of an external optical connector. Accordingly, a fiber receiving end, which is provided at a lower part of the APC receptacle, needs to be aligned at a predetermined position and a predetermined direction to achieve the maximum optical coupling. However, both of the angle and the direction of the APC receptacle are limited, resulting in complication and difficulty in manufacturing an APC receptacle TOSA compared to the PC receptacle TOSA.